JP2010258562A - Electret material, manufacturing method thereof, and electrostatic acoustic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing an electret material which improves the adhesion between a resin layer to be an electret layer and an electrode plate. <P>SOLUTION: The method for manufacturing an electret material includes: applying dispersing liquid which contains polytetrafluoroethylene particles and also contains 10 to 300 pt.wt. of polyether ether ketone particles in 100 pt.wt. of the polytetrafluoroethylene particles on the electrode plate and then drying the dispersing liquid; and further, burning the polytetrafluoroethylene particles and the polyether ether ketone particles to form a mixed resin layer on the electrode plate. After that, electrification processing is applied to the surface of the mixed resin layer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electret material used for an electrostatic acoustic transducer, a manufacturing method thereof, and an electrostatic acoustic transducer including the electret material.

  Conventionally, electret materials in which an electret layer is formed on an electrode plate have been used in electrostatic acoustic transducers such as earphones, headphones, and microphones. For example, in an electret condenser microphone (ECM) incorporating an IC element, the electret material is disposed facing the front side or the back side of the diaphragm.

  In the electret material, the electret layer is made of a fluororesin, and the electrical insulation and charge retention of the fluororesin are utilized. Such electret materials are conventionally punched into a desired shape by laminating an electrode plate and a fluororesin film, or by applying a fluororesin paint on the electrode plate and heating it. Then, it was obtained by performing a charging process (see, for example, Patent Document 1).

JP 2002-125297 A

  However, since the fluororesin generally has poor adhesion to other materials such as an electrode plate, when the fluororesin layer is formed on the electrode plate as described above, the fluororesin layer has a blade when punching at high speed. , And peeled off from the electrode plate, resulting in a problem that the yield decreased.

  Here, in the method in which the fluororesin coating is applied to the electrode plate and heated, it is also conceivable to apply an undercoat coating on the electrode plate in advance in order to improve the adhesion between the fluororesin layer and the electrode plate. However, when a general polyamideimide resin is used as the undercoat paint, delamination may occur during heating of the electret material or during heating after manufacture due to the difference in thermal expansion coefficient between the polyamideimide resin layer and the electrode plate. There is.

  An electrostatic acoustic transducer may be mounted on an electronic device such as a mobile phone, for example. From the viewpoint of automation, this mounting is a so-called reflow that solidifies after heating and melting previously disposed solder or the like. It is desirable to do so by processing. However, in an electrostatic acoustic transducer using an electret material that has been primed as described above, delamination of the electret material may occur during heating, and therefore reflow treatment cannot be performed. Therefore, the electrostatic acoustic transducer must be fixed to the electronic device manually, which leads to an increase in manufacturing cost.

  In view of such circumstances, the present invention provides a method for producing an electret material capable of improving the adhesiveness between a resin layer serving as an electret layer and an electrode plate, an electret material produced by this production method, and electrostatic sound. An object is to provide a converter.

  The inventor of the present invention has conducted extensive research to solve the above problems, and as a result, a resin layer is formed by applying a dispersion obtained by mixing PEFE fine particles to PTFE fine particles on an electrode to form a resin layer. It has been found that the adhesion with the electrode plate can be improved. However, if the amount of PEEK fine particles increases too much, the surface potential of the electret layer when heated to a high temperature by a reflow process or the like is greatly reduced. The present invention has been made from such a viewpoint.

  That is, the present invention relates to a method for producing an electret material used for an electrostatic acoustic transducer, comprising polytetrafluoroethylene fine particles, and polyether ether ketone fine particles based on 100 parts by weight of the polytetrafluoroethylene fine particles. A dispersion containing 10 to 300 parts by weight is applied on the electrode plate and then dried, and the polytetrafluoroethylene fine particles and the polyether ether ketone fine particles are fired to form a mixed resin layer on the electrode plate. There is provided a method for producing an electret material, including a step of performing a charging process on the surface of the mixed resin layer.

  In addition, the present invention comprises an electrode plate, and an electret layer formed on the electrode plate and containing polytetrafluoroethylene and polyetheretherketone at a weight ratio of 100: 10 to 100: 300. Providing materials.

  Furthermore, this invention provides an electrostatic acoustic transducer provided with said electret material and the diaphragm facing this electret material.

  According to the present invention, the adhesion between the mixed resin layer serving as the electret layer and the electrode plate can be improved by mixing the polytetrafluoroethylene fine particles and the polyether ether ketone fine particles. Moreover, since the amount of the polyether ether ketone fine particles is suppressed to a predetermined amount or less, it is possible to suppress a decrease in the surface potential of the electret layer when heated to a high temperature.

It is sectional drawing of the electret material which concerns on one Embodiment of this invention. It is sectional drawing of the electrostatic acoustic transducer using the electret material shown in FIG.

  The manufacturing method of the present invention is for manufacturing an electret material 1 in which a mixed resin layer 3 is formed on an electrode plate 2 as shown in FIG. 1. As an example, a preparation process, a formation process, And charging step.

(Preparation process)
In the preparation step, a dispersion containing polytetrafluoroethylene (hereinafter referred to as “PTFE”) fine particles and polyether ether ketone (hereinafter referred to as “PEEK”) fine particles is prepared.

  The mixing ratio of the PTFE fine particles and the PEEK fine particles is preferably 10 to 300 parts by weight of the PEEK fine particles with respect to 100 parts by weight of the PTFE fine particles. When the ratio G2 / G1 of the weight G2 of the PEEK fine particles to the weight G1 of the PTFE fine particles is less than 10%, the adhesion between the mixed resin layer and the electrode plate described later does not improve so much, and the ratio G2 / G1 exceeds 300%. This is because the charge retention with respect to heat of the electret material is reduced. A more preferable mixing ratio is 20 to 100 parts by weight of PEEK fine particles with respect to 100 parts by weight of PTFE fine particles.

  For example, the dispersion liquid can be produced as a mixed liquid by mixing a first dispersion liquid in which PTFE fine particles are dispersed in a dispersion medium and a second dispersion liquid in which PEEK fine particles are dispersed in a dispersion medium at a predetermined ratio. it can.

  The dispersion medium of the first dispersion liquid is, for example, water. As such a dispersion, various commercially available products prepared by an emulsion polymerization method are available, and these can be used. For example, Polyflon D-1 manufactured by Daikin Industries, Ltd., Fullon AD938L manufactured by Asahi Glass may be used.

  The specific gravity of the first dispersion is preferably 1.2 to 1.6, more preferably 1.3 to 1.5.

  The dispersion medium of the second dispersion liquid is, for example, water. As such a dispersion, various commercially available products are available and can be used. For example, No. manufactured by Victrex MC 804 or the like may be used.

  The specific gravity of the second dispersion is preferably 1.1 to 1.3, and more preferably 1.1 to 1.2.

  In addition, for example, a dispersion containing PTFE fine particles and PEEK fine particles may be prepared by adding PEEK fine particles after adding a surfactant to the first dispersion in which PTFE fine particles are dispersed in a dispersion medium. Is possible.

(Formation process)
In the forming step, a mixed resin layer is formed on the electrode plate using a dispersion containing PTFE fine particles and PEEK fine particles. Specifically, the dispersion is applied on the electrode plate and then dried, and the PTFE fine particles and the PEEK fine particles are fired.

  As the electrode plate, a metal plate made of stainless steel, aluminum, steel, copper, titanium, and alloys thereof can be used. Alternatively, the electrode plate may be a metal foil supported on a substrate, for example. That is, the electrode plate of the present invention may be made of a thin metal, and the thickness is not particularly limited. However, the thickness of the electrode plate is preferably 100 to 300 μm from the demand for downsizing of the electret material. Moreover, in order to improve the adhesiveness with the mixed resin layer, it is preferable that the electrode plate does not adhere oils and fats.

  A known method can be used to apply the dispersion liquid on the electrode plate. For example, it may be performed using a dispenser, or may be performed by a spin coating method or a printing method. Alternatively, the dispersion may be applied onto the electrode plate by masking one surface of the electrode plate and immersing the electrode plate in the dispersion (dipping).

  After the dispersion is applied on the electrode plate, the dispersion medium is removed from the dispersion and the dispersion is dried. Drying is performed, for example, by placing the electrode plate coated with the dispersion in a temperature (for example, 180 ° C.) environment lower than the PTFE melting point (327 ° C.) for a predetermined time (for example, 10 minutes).

  Thereafter, the PTFE fine particles and the PEEK fine particles are fired. Firing is performed, for example, by placing the electrode plate carrying the dried dispersion (PTFE fine particles and PEEK fine particles) in a temperature environment equal to or higher than the melting point (343 ° C.) of PEEK for a predetermined time (for example, 10 minutes). Thereby, a mixed resin layer is formed on the electrode plate. The temperature during firing is preferably 380 ° C. or higher. After firing, the electrode plate is cooled to room temperature.

  In addition, it is preferable that the film thickness of the mixed resin layer to form is 10-100 micrometers. This is because within this range, the electret material can be reduced in thickness and size while maintaining the characteristics of the electret material. A more preferable thickness of the mixed resin layer is 10 to 50 μm.

  As described above, a large sheet (uncharged electret material) having a mixed resin layer formed on an electrode plate is produced. This large sheet is cut into a predetermined size, for example, by punching. At this time, since the mixed resin layer is firmly bonded to the electrode plate due to the influence of PEEK, the mixed resin layer is prevented from peeling from the electrode plate.

(Charging process)
In the charging step, the surface of the mixed resin layer in the uncharged electret material cut to a predetermined size is subjected to a charging process to form the mixed resin layer as an electret layer. The charging process is performed by polarization-charging the surface of the mixed resin layer by, for example, corona discharge. Note that an aging treatment may be performed after the charging step.

  Through the above steps, the electret material 1 as shown in FIG. 1 can be obtained. The electret layer 3 of the electret material 1 contains PTFE and PEEK in a weight ratio of 100: 10 to 100: 300.

  When the electret layer is composed of only a fluororesin, there is a method in which an undercoat paint is applied to the electrode plate in advance in order to improve the adhesion between the electrode plate and the electret layer. In that case, a polyamide-imide resin is used as the undercoat paint. When this polyamideimide resin is used, delamination tends to occur when the electret material is heated due to the difference in coefficient of thermal expansion between the electrode plate and the polyamideimide resin layer.

  On the other hand, when the electret layer is made of PTFE and PEEK, high adhesion between the electrode plate and the electret layer can be obtained, and delamination hardly occurs during heating.

  Moreover, by using PTFE as the fluororesin, it is possible to impart excellent functions such as antifouling property, chemical resistance, water repellency, weather resistance and the like to the surface of the electret material without impairing the flexibility of the electret material. It is possible to make the forming process relatively easily.

  The electret material obtained by the production method of the present invention is suitably used for an electrostatic acoustic transducer. As an example, FIG. 2 shows an ECM 10 using the electret material 1. The ECM 10 shown in FIG. 2 is of the back electret type, and the electret material 1 is disposed to face the back surface of the diaphragm 4. Specifically, the ECM 10 is laminated in the shield case 9 from the bottom to the top, the circuit board 7 on which the IC element 75 is mounted, the IC element 75, the back electrode substrate 6 that supports the electret material 1, the spacer 5, a diaphragm 4, and a support frame 8.

  The electrostatic acoustic transducer includes a hearing aid, an ultrasonic sensor, an acceleration sensor, and the like in addition to a microphone, an earphone, and a headphone.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not restrict | limited to these Examples at all.

Example 1
Commercially available PTFE dispersion (Asahi Glass Co., Ltd. AD938L (PTFE fine particle concentration 60 wt%)) 1.0 kg is mixed with 0.2 kg of commercially available PEEK dispersion (Victory MC Co., No. 804 (PEEK fine particle concentration 30 wt%)) 0.2 kg. Then, the mixture was stirred to produce a dispersion (mixed solution) in which 10 parts by weight of PEEK fine particles was added to 100 parts by weight of PTFE fine particles.

  A commercially available aluminum foil having a thickness of 200 μm (made by Toyo Aluminum Co., Ltd., rough surface soft foil) was used as the electrode plate, and one side of this electrode plate was masked with a masking adhesive tape. The electrode plate was passed through the produced dispersion at a dipping rate of 100 mm / min, and the dispersion was applied to one side of the electrode plate. Next, the electrode plate was placed in an 80 ° C. environment for 10 minutes to dry the dispersion, and then the masking adhesive tape was peeled off. Thereafter, the PTFE fine particles and the PEEK fine particles were baked by placing the electrode plate in an environment of 380 ° C. for 10 minutes. After firing, the electrode plate was cooled to room temperature. As a result, an uncharged electret material in which a mixed resin layer having a film thickness of 25 μm was formed on an electrode plate having a thickness of 200 μm was obtained.

(Example 2)
Uncharged electret in the same manner as in Example 1 except that 0.5 kg of PTFE dispersion was mixed with 1.0 kg of PEEK dispersion to produce a dispersion having 100 parts by weight of PEEK fine particles per 100 parts by weight of PTFE fine particles. The material was obtained.

(Example 3)
Uncharged electret in the same manner as in Example 1 except that 1.5 kg of PEEK dispersion was mixed with 0.25 kg of PTFE dispersion to produce a dispersion having 300 parts by weight of PEEK fine particles per 100 parts by weight of PTFE fine particles. The material was obtained.

(Comparative Example 1)
A commercially available aluminum foil having a thickness of 200 μm (made by Toyo Aluminum Co., Ltd., rough surface soft foil) was used as the electrode plate, and one side of this electrode plate was masked with a masking adhesive tape. This electrode plate was passed through a commercially available PTFE dispersion (AD938L manufactured by Asahi Glass Co., Ltd.) at a dipping speed of 100 mm / min, and the PTFE dispersion was applied to one side of the electrode plate. Next, the electrode plate was placed in an 80 ° C. environment for 10 minutes to dry the dispersion, and then the masking adhesive tape was peeled off. Thereafter, the PTFE fine particles were fired by placing the electrode plate in an environment of 380 ° C. for 10 minutes. After firing, the electrode plate was cooled to room temperature. As a result, an uncharged electret material in which a PTFE layer having a thickness of 25 μm was formed on an electrode plate having a thickness of 200 μm was obtained.

(Comparative Example 2)
Uncharged electret in the same manner as in Example 1 except that 0.1 kg of PTFE dispersion was mixed with 1.0 kg of PEEK dispersion to produce a dispersion having 500 parts by weight of PEEK fine particles with respect to 100 parts by weight of PTFE fine particles. The material was obtained.

(Comparative Example 3)
Uncharged electret in the same manner as in Example 1, except that 0.1 kg of PEEK dispersion was mixed with 1.0 kg of PTFE dispersion to produce a dispersion having 5 parts by weight of PEEK fine particles with respect to 100 parts by weight of PTFE fine particles. The material was obtained.

(test)
The following tests were conducted on the uncharged electret materials of Examples and Comparative Examples.

  First, the surface of the resin layer in the uncharged electret material was polarized and charged by negative corona discharge at 25 ° C., and these layers were made into electret layers (an electret material was produced). Thereafter, the surface potential residual rate of the electret layer was measured as follows.

  The surface potential of the electret layer immediately after the charging treatment was measured with a surface potential meter (Model 244 manufactured by MONORO ELECTRONICS). Next, the electret material was placed in an environment of 210 ° C. for 30 minutes (load test), and the surface potential of the electret material thereafter was measured in the same manner. This operation was repeated three times. Then, the ratio of the surface potential after the first to third load tests with the surface potential of the electret material immediately after the charging treatment as a reference (100%) was calculated as the surface potential remaining rate (%).

  Further, a cross-cut test was performed on the uncharged electret materials of the examples and comparative examples. The cross cut test is a resin layer after the adhesive layer is applied and peeled off on the resin layer after making cuts reaching the electrode plate surface through the resin layer according to JIS K5600-5-6 The adhesion state of was visually observed. The number of wrinkles formed by the grids was 100. For example, when the resin layer remained on 50 wrinkles after the tape was peeled off, it was evaluated as 50/100.

  The results of the above test are shown in Table 1. In Table 1, the ratio G2 / G1 of the weight G2 of the PEEK fine particles to the weight G1 of the PTFE fine particles in the dispersion is shown in%.

  In Comparative Example 1 in which the PTFE dispersion was applied on the electrode plate, it was confirmed by a cross-cut test that the PTFE layer was peeled off from the electrode plate. In Comparative Example 2 using a dispersion containing PTFE fine particles and PEEK fine particles, the cross-cut test result was good, but the surface potential residual rate of the electret layer after the load test because the amount of PEEK fine particles was too large. Decreased significantly. In Comparative Example 3 in which a dispersion containing PTFE fine particles and PEEK fine particles was used, but the amount of PEEK fine particles was too small, it was confirmed that the mixed resin layer was peeled off from the electrode plate by a cross-cut test.

  On the other hand, in Examples 1 to 3 using the dispersion containing PTFE fine particles and an appropriate amount of PEEK fine particles, the cross-cut test results are good and the surface potential residual rate of the electret layer after the load test is reduced. Was able to be suppressed to some extent.

DESCRIPTION OF SYMBOLS 1 Electret material 2 Electrode board 3 Electret layer 10 ECM (electrostatic acoustic transducer)

Claims (6)

A method for producing an electret material used in an electrostatic acoustic transducer,
A dispersion containing 10 to 300 parts by weight of polytetrafluoroethylene fine particles and polyether ether ketone fine particles with respect to 100 parts by weight of the polytetrafluoroethylene fine particles is applied on an electrode plate and then dried. Firing the tetrafluoroethylene fine particles and the polyether ether ketone fine particles to form a mixed resin layer on the electrode plate;
Applying a charging treatment to the surface of the mixed resin layer;
The manufacturing method of the electret material containing this.   The manufacturing method of the electret material of Claim 1 which mixes the 1st dispersion liquid containing polytetrafluoroethylene microparticles | fine-particles, and the 2nd dispersion liquid containing polyetheretherketone microparticles | fine-particles, and produces | generates the said dispersion liquid.   The manufacturing method of the electret material of Claim 1 or 2 whose film thickness of the said mixed resin layer is 10-100 micrometers.   The manufacturing method of the electret material as described in any one of Claims 1-3 which bakes the said polytetrafluoroethylene fine particle and the said polyether ether ketone fine particle at 380 degreeC or more. An electrode plate;
An electret layer comprising polytetrafluoroethylene and polyetheretherketone formed on the electrode plate in a weight ratio of 100: 10 to 100: 300;
An electret material.   An electrostatic acoustic transducer comprising the electret material according to claim 5 and a diaphragm facing the electret material.

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